Convection section



April 25,- 1944. F, H PRAEGER 2,347,433

CONVECTION SECTION Filed Sept. 23. 1942 INVENTOR.

Few/wf Pe/Qfcv'fe 197' TQENEY Patented Apr. 25, 1944 CONV ECTION SECTION Frank H. Praeger, Merion, Pa., assignor to Alcorn Combustion Company, Philadelphia, Pa., a corporation of Delaware Application September 23, 1942, Serial No. 459,466

3 Claims. (Cl. 122-356) My invention relates to uid heaters of the tubular type and has for an object the provision of a convection section, which for a given number of tubes has a much greater efficiency than heretofore obtained.

fer to include one or more rows of tubes between the convection section and the radiant section of the heater arranged in the usual manner in order to avoid overheating of the tubes in the 5 more ecient portion of the convection section In many heaters, particularly those used for which embodies my invention. the heating of petroleum and its derivatives, the For a more complete understanding of my inhot gases and/or the products of combustion vention, reference is to be had to the accomiiow from a nre chamber into a convection secn panying drawing in which: tion where the transfer of heat from the hot Fig. l is a sectional elevation of a part of a gases to the oil is largely by convection. Usually heater embodying my invention in one form the convection section consists of a relatively thereof; large number of tubes arranged to be washed Fig.' 2 is a fractional View of one means of by the gases, and through the walls of the tubes supporting a bale from a fluid conducting tube; heat is conducted to the fluid flowing therein. Fig. 3 is a fractional view of a heater and To increase the transfer by convection, such shows a sectional view of a convection section tubes have been provided with ns and gill embodying a preferred form of my invention; rings; and other expedients have been resorted to and in an endeavor to increase the transfer of heat Fig. l is a fractional View of a means for by convection to the uid traversing the tubes. 2o supporting a central baie from a pair of fluid In carrying out my invention in one form conducting tubes. thereof, I take advantage of the fact that there Referring to the drawing, I have shown my is a relation between the amount of heat which invention in one form as applied to av single endmay be transferred by radiation and the area of red heater, that is, one where a plurality of the surface in view of the tubes, which surface fuel burners ID are arranged to direct fuel into is not covered, shielded or obscured by other a plurality of muffles II, distributed along one heat absorbing devices such as tubes. I also side I2 of the heater. Partial combustion of take advantage of the radiant heat which is the fuel is completed within the muffles, formed present in the convection gases and provide for of super-refractory material, and from each transfer thereof directly to the heater tubes. Inutile Still-burning gases and products of Com- Heretofore, it has been generally believed that bustion are directed generally horizontally after the convection gases have passed beyond across the nre chamber I3 and intermediate a the first few rows of convection tubes, transfer bank of floor tube I4 and an upwardly sloping of heat by radiation is of inconsequential degree. bank of roof tubes I5. The rear wall I6, to- In accord with my invention, however, the transgether with an upwardly rising wall I1 from fer by radiation may be maintained at an unthe sloping roof I8, form a convection section expectedly high rate and at the same time the I9, only a, pari; of which is shown, transfer by convection may also be maintained The convection gases including the products at 2 high rate- In Consequence, it S Possible of combustion are subject to stack-draft and, t0, absorb the Same amount 0f heat With a fewer 40 after their horizontal travel over and above the number of tubes, al1 other conditions being equal. poor tubes i4, exit from the me chamber |3 by In the Preferred form 0f my invention, TOWS way of the convection section I9. They first of tubes eXtend in double Zig-Zag relation ow between the tubes 20 and thence between through the Convection Section and Side bellies, the tubes 2I and 22 of additional horizontally and central baiiles alternating herewith, produce disposed rows. The tubes of rows 2li-22 are in tWO SinllOUS Paths Whoh folloW the junotllleS of staggered relation with each other and are subadacent rows and which Cross and reCrOSS the ject both to radiant heat from nre chamber a Zig-Zeg IOWS. By providing vthe angular or Zigl and to convection heat.

Zag arrangement of the IOWS of tubes, a rele- From the row 22, additional tubes are artively large amount of free space is provided ranged in rows 23, 24 and 25 which zig-zag and there iS a Substantial transfer 0f heat by through the convection section I9. A baffle 26 radiation t0 the tubeS- BY reason of the now extends from the wall I'I outwardly toward the directing function of the baffles there is eiend-tube 23A of the row 23. Between the side cient transfer of heat by convection to the tubes. or free-end of the bam@ 25 and the wan |6 of the There are dead SPaCeS- However', I pleu convection section, a flow passage is provided.

The combustion gases are conned to flow through that passage and across the angularly disposed row of tubes 23. A second baille 21 extends from the wall i6 toward the juncture of rows 23 and 24. Hence the gases which have passed between the first few tubes of the row 23 mustreverse their direction again-to cross the row 23. The gases pass downwardly between tubes 23 and eifectively wash the entire circumferential areas of tubes 23. The gases then move around the free end or side of baille 21 and flow upwardly across the first few tubes of the row 24. Another bale 28 -extends `from the wall I1 outwardly toward thejunctureof the rows 24 and 25. This baille redirects the gases so that they must again reverse their direction of flow again to cross the row 24. Theabove-described flow, by reason of the baille l29, is repeated and it will be understood that additional rows of tubes and baiiles may be provided in the remainder kof the convection section (not shown).

It will be observed that gases flowing between adjacent tubes 20, divide around the tubes 2l of the next adjacent row vandit is well understood by those skilled in the art that the maximum transfer of heat occurs along relatively restricted fractions of the'circumferential areas of each tube. However, inaccord with rnyinvention, the flow-directing baffles 26-29 produce a sinuous flow of the gases along the'zig-zag arrangement of tubes. The gases cross the tubes of each row, vsuch as 23, in one direction and they then cross the tubes of that row in the opposite direction, andthey then recross the tubes of the sameV row. In this manner the gases effectively wasli substantially the entire circumferential'areas of eachtube. There are no dead spaces. There are no tubes located out of the path of the gases.

These rdesirable results are brought about by reason of the angular relation of each row with respect to the path ofthe gases when considered in connection with that row. Considering the flow from above the row 23 and below the baille '21, the gases mustl flowto the left, thence downwardly between the tubes of the row 23 and thence upwardly around the tubes and a similar circuitous route is followed in the flow of the gases'through the Vrows 24 and 25. The result is convective contact with substantially the en- .'tire circumferential area of each convection tube.

Besides this intimate, efficient contact of the 'gases about the tubes, the relatively large tubefree areas have a beneficial eifect in re-radiating heat to the' tubes. There is also a substan- `tial transfer of heat by radiation from the' gases.

The combined resultof the increased transfer by convection and the transfer by radiation makes possible the use of only 52 convection tubes'to Aperform a heat absorbing duty which heretofore `r'eq'uiredO tubes in a conventional staggered arrangement.

In'calcula'ting the heat absorbed 'in' a convection section, determination 'is first made of the K factor, "denned as the vBritish thermal units per square foot of heat absorption'surface'per A'hour per'degree of temperature difference F.) between the convection gases and the liquid being heated. Inaccord with my invention, -the K"fa`ctor is'incr'eased as much as 100%, which I `are to be taken as representative of the sloping roofs which extend over a pair of re chambers. The gases and products of combustion fromboth nre chambers flow through the central Vconvection section 30 provided with rows of t'ubes'33, 34 and35 disposed in the inlet portion. The convection section 30 is subject to stackdraft. The first three rows of tubes 33-35, disposedin staggered relationship, serve the same purposes as described in connection ywith the rows of tubes 20,f2| and 22 of Fig. 1. In-this embodiment of my invention rows of tubes'ex- Vtend through the convection section 30in double zig-Zag relationship. A central'bafl'le-31 yextends across the convection section and after the gases have passed through the-row35 of tubes the baille causes them to divide and to flow outwardly to the sides thereof and towards the respective walls 38' and39 of the convectionsection. 'From the respective-walls 38 and 39 rows of tlubes extendV angularly toward each other and toward their juncture with rows 42 and 43. Thelatter rows angularly extend inthe opposite direction andrespectively back toward the walls 38 andA 39. `From the juncture of rows 42 andv 43 vwith rows 44 and 45, the rows 44 and 45 extend angularly vtoward the central Vpart ofthe convection section 30. Similarly, rows 46 and 48 form a continuation of the zig-Zag row on the left hand side of the convection section-30, and'rows 41 and`49 forma continuation of the zig-zag row along the rig-ht hand part of the convection section 30.

The tubes in the zig-zag rows have their axes disposed along the sides of triangles, the bases of each-of which extends longitudinally of y-the convection section. n

This triangular relationshipv is present in the arrangement of Fig. 1 aswell as in Fig. 3. Bafes 50,51 and 52 extend from the side wall.38.to

ward'the` respective apices-between the rows or triangle sides 40-42, 44--46 and 48. Similarly baiiles 53, 54 and 55 extend from the side wall l39 between the triangle sides lll-'43, 45-41 and the lowerthree rows 33-35 divide aroundthe opposite sides of baffle 31. The respective streams of gasesgcross' and recrossthe rows'40 andf4l. The streams then joinftogether and passbetween and around the tubesdisposed at the junctures of rows 40-42'and-4|43. Thefgases then4 divide for flow around oppositev sides of the 1baille 51. They cross andvrecrossithef'rowsfdliand 43 and the. foregoing. procedure is repeat'edflfor each row of tubes.

It will be observed that the baille 31 is spaced a considerable distance away from, as above, the row of tubes 35. The intervening space provides free ow of the gases and tubes are not located in that region since they would not be efficiently heated.

The baille 51, as shown in Fig. 4, may be provided with downwardly extending arms 60 and El which terminate in semi-circular members 62 and 63 which may nest over tubes 42A and 43A of the rows 42 and 43. If desired, additonal supporting means may be provided on the intermediate tube sheets (not shown) normally utilized for the support of the convection tubes.

The baille 31 of Fig. 3 will, of course, be provided with longer extensions for support from two or more of tubes 35.

The side baffles of Figs. l and 3 are preferably supported at one end from the side walls of the respective convection sections. The free side or end of each side baille may be provided with an extension 85, Fig. 2, provided with a semi-circular member 65 for engagement with a tube of one of the rows.

Without aifecting the described relation of the tubes with respect to the flow of the convection gases, fluid may be circulated serially through the tubes as illustrated in Fig. 1, or the tubes may be connected for parallel flow as shown in Fig. 3. For example, it may enter the tubes in the convection section through the inlets 1U and 1I and the divided streams may exit through the outlet lines 12 and 13 which may be transfer lines connected to other tubes in the double-end fired heater, such for example as the roof tubes 14 only three of which are illustrated. The tubes may also be connected for other desired flow arrangements such as series-parallel ilow.

While I have shown embodiments of my invention, it is to be understood, I do not limit myself thereto, since many modications may be made and I therefore contemplate by the ap pended claims to cover any such modications as fall within the spirit and scope of my invention.

What I claim is:

1. The combination with a heater having walls forming a convection section receiving gases and products of combustion from the heater, of horizontally extending iluid conducting heat absorbing tubes disposed only in rows which extend respectively from opposite walls of said convection section toward the center thereof and back again, the said rows extending in double zigzag relationship through said convection section, side bailles extending from said opposite walls toward the juncture of adjacent rows, central baffles a1- ternating with said side bailles to produce flow of said gases and products of combustion along double sinuous paths extending through the convection section which cross and recross said zigzag rows, and means interconnecting said tubes of each row for flow of fluid therethrough.

2. The combination with a heater, of walls forming a convection section having an inlet for combustion gases and an outlet subject to stackdraft, a plurality of rows of tubes in staggered relationship disposed across said inlet, a baille spaced substantially from said said tubes in the direction of flow of said gases and extending across the central portion of the convection section for dividing the convection gases, each division thereof ilowing around a side of said baille and adjacent one of said walls, and means ex tending through said convection section, which comprises a row of horizontal tubes extending from beyond each side of said baille angularly toward the central portion of said convection section, side bailles extending from each of said walls to restrict flow of gases to between said angularly disposed rows in the region where they approach each other, additional rows of horizontal tubes extending angularly from said central portion toward said walls, and a central baille for producing divided flow of said gases along paths generally coinciding with said last named angularly disposed rows, the said gases ilowing over and around the tubes of said rows.

3. The combination with a heater having walls forming a convection section receiving gases and products of combustion from the heater, of horizontally extending iluid conducting heat absorbing tubes disposed only in rows which extend respectively from opposite walls of said convection section toward the center thereof and back again, the said rows extending in double zigzag relationship through said convection section, side bailles extending from said opposite walls toward the juncture of adjacent rows, central baffles alternating with said side bailles to produce flow of said gases and products of combustion along double sinuous paths extending through the convection section which cross and recross said zigzag rows, each of said central bailles having structure extending downwardly and into supporting engagement with tubes for supporting each of said central bailles therefrom, and means interconnecting said tubes of each row for flow of iluid therethrough.

FRANK H. PRAEGER. 

